1. Field of the Invention
The present invention relates to a sliding correlator using a phase-shift in frequency domain to detect a pilot sequence with a time-division multiplexed pilot structure that meets Universal Terrestrial Radio Access Network Long Term Evolution (UTRAN LTE) requirements for cell acquisition and cell measurement.
2. Description of the Related Art
The synchronization channel (SCH) is for cell search. It consists of two sub-channels, a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH). The 10 ms frames of the P-SCH and S-SCH are divided into 15 slots, each of length 2560 chips. The synchronization channel is non-orthogonal to the other channels and is only switched on during the first 256 chips of each slot. The P-SCH is the same in all slots of the frame, where as the S-SCH changes every slot. This enables the mobile to reasonably quickly search for the P-SCH to establish the frame timing, and then use the S-SCH to find the slot timing. The sequence on the S-SCH also indicates which scrambling code is used in the cell.
Conventional algorithms to detect the S-SCH in 1.25 MHz may be best processed in a time domain providing that most sub-carriers in an orthogonal frequency division multiplexing (OFDM) symbol are allocated to an S-SCH code. A relatively small number of sub-carriers may be mapped to system information in the same OFDM symbol. For instance, in a 1.25 MHz narrow band, a pilot sequence of 16 sub-carriers may be mapped to one sub-carrier every five sub-carriers to pilots in the OFDM symbol (one permanent common pilot OFDM symbol, followed by six OFDM symbols containing data, and one dedicated pilot, in a time-division multiplexing (TDM) pilot structure with sub-frame of length 0.5 ms, as shown in FIG. 1). However, if similar time-domain (TD) algorithms are considered for pilot sequence detection, the performance of the algorithms is severely compromised by a relatively large number of non-empty sub-carriers mapped to system information or data in the OFDM symbol containing the pilot.
A conventional pilot sequence detection system may include a multiplexed (TDM) pilot structure that meets Universal Terrestrial Radio Access Network Long Term Evolution (UTRAN LTE) requirements. The S-SCH mapped proposed to pilot sequence provides using a scattered pilot structure.
As with S-SCH, a pilot sequence detection method may be used with decoding of system information common to all bandwidth carried by the pilot OFDM symbol, e.g., 1.25, 2.5, 5, 10, and 20 MHz. This is final check to ensure that pilot sequence is correctly detected. Decoding of system information requires simple channel estimation (i.e., multiplication of received pilot symbols by reference pilot symbols followed by frequency-domain FIR filter smoothing). As the number of sub-carriers allocated to common system information is rather small (e.g., around 60 sub-carriers), the code length is relatively small and decoding complexity may be kept low. It would be preferable to rely on false detection mechanism to avoid reading system information during (fast) cell measurements for handover.